RowJ

Glad sky did not fall!
Hit it as soon as you feel 1-2 shift..... should worth 1/10+.

RJ

DodgenIt

I really didnt think id have the fuel to push more then 60 lbs though. I know this isnt an exact way to figure it, but my fuel adds up to 505 hp, which loose rule of thumb being 1 lb for 10 hp, should be around 50 lbs boost. But more then 60?? Are the compounds that far out of tune?
Pre loosened, my big turbo want starting to spool till 10 lbs making the truck super laggy. Now the big one starts to spool at 5 lbs and I like it.
BUT dont like not knowing what im boostin too. I know I could get a 80 lb gauge but I dont get how Im hittin 60+ with my fuel.

Ya know RowJ, I was plannin on lockin up son as I hit 2nd, but while in the staging lanes I was reading Diesel Power mag and literally reading the article up front... What I learned.. from DPC 2011. The section titled... breakage can be avoided. Hahaha read that while 15 cars back from the line and decided to lock up a little later.

RowJ

With twins, your lowest EGT's and your best performance is with Secondary set for full boost and let your primary do what it will/can.
On HP, are you allowing for the additional 40-45 hp "released" by twins?
I would not worry about another gauge. You will find your making 60-62 psi if you get one. Been there and done that. You can tell by how quickly needle comes down if you back off just a hair.
You won't see more boost till you add another 100 hp.

All 24v CTD's making 550-650 hp make 58-64 psi, from my experience.

RJ

Tate

I think that goes out the window with twins. I was hitting 80 psi with my 12v, and I know I'm not at 800hp with it. If I was at 600 at the time, I was doing good.

DodgenIt

I hear ya Tate, that makes sense to me that it would be thrown off by the twins.

So I know for a fact my waste gate on the secondary is as loose as it can go, before I run out of rod and the waste gate is fully able to open with 0 resistance. Far as I can tell, the waste gate now starts to open at 5 lbs and is fully open by 30 lbs.

Should I tighten it up a little then? Make the secondary do a little more Work?

Wont that slow my spool up though too?

If my Secondary is set to what it was when I got it, (39 lbs) and Im toppin out at 60 lbs, so only 21 lbs from primary... I thought boost is supposed to be split equally between the two for the best drive pressure, egts, spool up and performance.

Tate

Do you have a gauge on your primary turbo? If you're just guessing you're running 21 out of the primary, you should double check. Mine runs at a consistent 2:1 overall to primary boost at full boost. Cruising, its more of a 3:1 ratio. Tighter wastegate will run the primary harder, you'll have a more response, but less pull. Looser wastegate, you'll lose response, but you'll get more power out of it. Its a fine line that you have to decide how you want it to react. A friend that we just put twins on his truck, had the wastegate real loose, it was all on the primary. It was hot and smoky, and could only pull 20 psi. That was with a small ball bearing Garrett and an S478.

Bersaglieri

My stock head/bolts have held up to 78psi so far. Not sure what I'm making power wise but I never run it over 6-8psi until it gets to operating temp. Plus I have close to stock timing at the moment.

-Dustin-

RowJ

John Todd... The Turbo Engineer at BD told me the secondary should be left as if it was a single (in your case - factory setting of 40 psi). With a decently matched pair, that will give you close to 2:1. This set up, whether 2:1 or not gives lowest EGT's and best spoolup, which is more important than an exact 2:1.

I believe more fuel would give you more primary boost; you've room to grow!
I wouldn't over think it....especially if no primary gauge.
Easy to weld a bung on the air tube between the two turbos. Don't need a permanent gauge. Just a test hole. Most accurate closer to the secondary.

RJ

DodgenIt

Im guessing, but im not.
The 39 from secondary 21 primary was just an example.
My waste gate is much looser now then it was from the factory.
But I am still some what guessing cause i set it using a compressor hose with gauge to the boost line which isnt very accurate ive been told.
I have a boost gauge for the primary on the way now. Bummer thing is my cold pipe is silicone so I cant drill/tap or weld to it. Im planning on drilling and tapping the compressor of the primary. just sucks cause uch more will have to come apart for that.

Ok, Im gonna tighten it up and bit and see how things run.
I am planning on the room to grow though. Hopefully by next fall I will have valve springs, drop in cam and some 200 hp sticks.

Mike Holmen

I rather have the primary load up harder than the secondary, you get way more air from the primary than what you can from the secondary. I've ran with an adjustable wastegate controller before, for that twin set-up 24psi was the sweet spot. I adjusted the pressure inside the cab controller, so it was easy to get everything balanced up.

Lots of variable going from turbine disk size, turbine A/R ratios to waste gate size, to nail down an exact wastegate pressure.

Usually when ever I ran more secondary, my drive pressure increased and would limit my top end power. Ya the truck was more responsive driver, mostly caase the secondary had more pressure on the wastegate, holding the flapper closed. No exhaust leak by thru the wastegate.

External wastegates really works well, fixs lots of twins issues.

As for boost pressure, I've lost head gaskets running orings, head studs and not run head studs. No cut and dry answers for that issue.

HOHN

True, because you are heating the air a lot more. So for the same amount of mass flow (lb/min of air) the pressure and temp are higher.

If you actually had 10hp per psi, that would be a VERY efficient twins setup. Like unrealistically efficient.

JH

DodgenIt

I did notice more air flow and barely lower egts running the primary harder.

Really im just trying to find that sweet spot between good spool up for towing around town, but good top mid and top end on the track. Cause thats the best part about compounds, gettin it all!! Haha as long as your tuned right.

Mike what kinda controller where you using. That sounds easier to work with, Id like to hear more about it please.

As for now, I tightened up the waste gate on the secondary just a hair, (about in the middle of how tight it was when first compounded and as loose as it could go) Im liking it around town, seems to move a little more air quicker makin less smoke... We'll see how it goes for weekend on the edge race and dyno next week.

Mike Holmen

Depends on what turbos you run as what boost you have. Some turbo just run out of air and you just walk up the choke area into overspeed.

Choke = over heated inlet air = egt's

DodgenIt

I dont think I have enough fuel to over speed them. Maybe the secondary if the waste gate was super tight, but its far from that.

And my egt's dropped almost 300* down to a nice 1400 so I definantly dont think over speeding is the issue.

DodgenIt

So here's something wierd... I dyno'd at weekend on the edge yesterday, and put down the same hp as last year!
When runnin my current secondary as a single, I was maxin it out on the track with a 14.40 run. I tried and tried but couldnt get any faster.
Since compounds, Ive got it down to 13.80 with another 10th or so shaveable.

How can I be .6 seconds faster, with the same hp. Everything else on the truck is the same. I put down a little more torque but my 60 ft times are the same as before too so its not there that im makin the differance.

Im confused.